In LTE (Long Term Evolution) and a successor system (for example, also referred to as LTE-Advanced, FRA (Future Radio Access), 4G and the like) to LTE, D2D (Device to Device) techniques have been studied in which user terminals directly transmit and receive signals to/from one another by bypassing a radio base station (for example, Non-patent Document 1).
In inter-terminal direct signal transmission/reception (D2D signal transmission/reception), the user terminal performs D2D discovery to discover another communicable user terminal and inter-terminal communication (D2D communication). In D2D discovery, based on a resource designation method for discovery signal transmission, Type 1 (collision type) discovery and Type 2 (non-collision Type) discovery have been studied.